Microstructural evolution effects on the density of carbon nanotube fibers

In this study, we investigate structural change in wet-spun carbon nanotube (CNT) fibers and explore the resulting changes in density and tensile strength. Given the presence of chlorosulfonic acid (CSA) inside the fiber and the evolution of tubular shape, the difference between the experimental density of CNT fibers and the theoretical density of individual CNTs can be reasonably approximated. During the heat treatment of pristine CNT fibers at 1400 °C, the capillary force induced by removal of CSA between among CNTs leads to the polygonization of the circumference of individual nanotubes. This morphological transformation results in the improved tensile strength and increased density by enlarging the contact area among CNTs and reducing the occupied volume. The demonstration of correlation between CNT structure and density can offer insights into the manufacturing and applications of high-performance CNT fibers.